1. Technical Field
Illustrative embodiments described in this patent specification generally relate to an image forming apparatus such as a copier, a printer, or a facsimile machine that forms a toner image on a recording medium using an electrophotographic method, and more particularly, to a guide device to convey the recording medium having the toner image fixed thereon by a fixing device, and a method for controlling the image forming apparatus.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
The fixing device generally includes a rotatable fixing member such as a rotatable fixing roller or a rotatable fixing belt, each heated, and a rotatable pressing member such as a rotatable pressure roller or a rotatable pressing belt, pressed against the fixing member. A recording medium such as a sheet having an unfixed toner image thereon is passed between the fixing member and the pressing member, so that heat and pressure are applied to the toner image to melt and fix the toner image onto the sheet.
Increasingly, higher operating speeds, higher productivity, and greater compactness are required of image forming apparatuses. In order to meet such requirements, expansion of a nip that sandwiches a recording medium such as a sheet between the fixing member and the pressing member to apply heat and pressure to the sheet has been examined in a belt fixing method. For example, fixing devices often include additional rollers or members to wind the fixing belt or the pressing belt around the fixing roller or the pressure roller in order to extend the nip, or widen the nip, formed between the fixing roller and the pressure roller with the fixing belt or the pressing belt therebetween. The intention is simply to expand the area of contact between the fixing member and the pressing member, in order to achieve superior fixing performance, higher operating speed, and higher productivity.
However, because higher heat and greater pressure are applied to the sheet at the nip in the above-described fixing devices in order to achieve higher operating speed, sheets passing through the nip tend to curl as a result, and this curling may cause a sheet jam or folding of the sheet when the curled sheet enters a conveyance mechanism provided downstream from the fixing device. The above-described problem is particularly prominent in a case in which a gloss-imparting device, having a second nip between two rotary members of its own for imparting glossiness to the toner image formed on the sheet and also serving as the conveyance mechanism, is provided closer to the fixing device.
Further, a guide member for guiding the sheet is usually provided at an exit of the fixing device. When the curled sheet is discharged from the above-described fixing device, the sheet may collide with the guide member, wrinkling the sheet and (in duplex printing) leaving faint images on a back side of the sheet.